I. Field of the Invention
This invention relates generally to a system for interfacing a remote process variable sensor/transmitter to a local control system, and more particularly to a fiber-optic interface system in which power for the remote transmitter and associated interfacing electronics is provided by a light source located at the local site and in which data is transmitted, via a fiber-optic link, from the remote to the local site.
II. Discussion of the Prior Art
The Jensen et al. U.S. Pat. No. 5,258,868 describes an optical process variable transmitter of the type in which optical energy is transmitted from a local source to a remotely located process variable transmitter where it is converted at the remote location to electrical energy to power the remote electronics and in which the process variable information is also sent over a fiber-optic link to the local site. The system described in the Jensen et al. patent is deficient in not providing transmission of both analog and digital information nor does it provide adequate safeguard against possible eye damage to a technician if the optical fiber for transmitting the optical energy to the remote site is not connected to the converter circuitry. Moreover, the system described in the Jensen et al. patent is wasteful of optical energy. If a laser is used as the light source at the local site and the power it delivers to the remote site is not properly optimized, it results in a shortened life for the expensive laser employed.
Accordingly, it is a principal object of the present invention to provide an improved system for interfacing a remote process variable sensor/transmitter to a local control system in which optical power delivered from the local site is used to power the transmitter and electronics at the remote site.
A further object of the invention is to provide a light powered interface for a remote process variable transmitter that allows the simultaneous transmission of both analog and digital information from the PV transmitter to the local site.
Another object of the present invention is to provide a system of the type described in the foregoing object which incorporates a microprocessor-based controller at both the local site and the remote site where the microcontrollers oversee the delivery of optical power between the two sites.
Yet another object of the invention is to provide, in a system of the type described, a means whereby high intensity optical energy cannot be transmitted from the local site to the remote site unless the fiber-optic link is properly connected between the two.
Still a further object of the present invention is to provide a system of the type described in which the power delivered to the remote site by the optical light source (laser transmitter) at the local site is controlled by information provided to the local site by the remote site concerning the minimum power level necessary for operating the electronics at the remote site.